I am autistic and never had the MMR vaccine, which was not approved in the U.K. at the time. in fact, I was never vaccinated against mumps, because my parents felt the vaccine that *was* available wasn't worth it (I wasn't alone. It was a crappy vaccine).

I probably had asymptomatic mumps (I was exposed and never got sick so we thought I was immune, but we now know that mumps has about a 50% asymptomatic rate, so that's much more likely).

But never had that vaccine. It's *genetic*.